Five Prime Therapeutics (FPRX) 10-Q 5 Nov 15 2015 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3
Trading Symbol	FPRX
Entity Registrant Name	FIVE PRIME THERAPEUTICS INC
Entity Central Index Key	1,175,505
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		27,503,839

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 36,956	$ 15,267
Marketable securities	146,458	133,787
Receivable from collaborative partners	1,666	410
Prepaid and other current assets	5,454	1,794
Total current assets	190,534	151,258
Property and equipment, net	4,030	3,794
Other long-term assets	409	579
Total assets	194,973	155,631
Current liabilities:
Accounts payable	1,565	1,096
Accrued personnel-related expenses	4,280	4,618
Other accrued liabilities	4,033	1,531
Deferred revenue, current portion	12,119	11,938
Deferred rent, current portion	743	632
Total current liabilities	22,740	19,815
Deferred revenue, long-term portion	45,173	48,628
Deferred rent, long-term portion	1,057	1,514
Other long-term liabilities	$ 368	$ 469
Commitments
Stockholders' equity:
Common stock	$ 26	$ 22
Preferred stock
Additional paid-in capital	$ 361,051	$ 274,180
Accumulated other comprehensive income	37	1
Accumulated deficit	(235,479)	(188,998)
Total stockholders' equity	125,635	85,205
Total liabilities and stockholders' equity	$ 194,973	$ 155,631

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Collaboration and license revenue	$ 5,858	$ 6,059	$ 16,460	$ 14,586
Operating expenses:
Research and development	24,720	9,803	49,241	30,602
General and administrative	5,213	3,360	14,029	9,664
Total operating expenses	29,933	13,163	63,270	40,266
Loss from operations	(24,075)	(7,104)	(46,810)	(25,680)
Interest income	107	57	332	148
Other expense, net	(3)	(41)	(3)	(66)
Net loss	$ (23,971)	$ (7,088)	$ (46,481)	$ (25,598)
Basic and diluted net loss per common share	$ (0.93)	$ (0.33)	$ (1.82)	$ (1.24)
Shares used to compute basic and diluted net loss per common share	25,825	21,521	25,532	20,619

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (23,971)	$ (7,088)	$ (46,481)	$ (25,598)
Other comprehensive income:
Net unrealized (loss) gain on marketable securities	(35)	19	36	60
Comprehensive loss	$ (24,006)	$ (7,069)	$ (46,445)	$ (25,538)

Condensed Statement of Cash Flo

Condensed Statement of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating activities
Net loss	$ (46,481)	$ (25,598)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,275	1,154
Loss on disposal of property	3	41
Stock-based compensation expense	5,056	2,230
Amortization of premium on marketable securities	1,491	1,075
Changes in operating assets and liabilities:
Receivable from collaborative partners	(1,256)	205
Prepaid, other current assets, and other long-term assets	(3,490)	(539)
Accounts payable	469	324
Accrued personnel-related expenses	(338)	149
Deferred revenue	(3,274)	17,560
Deferred rent	(346)	(412)
Other accrued liabilities and other long-term liabilities	2,401	373
Net cash used in operating activities	(44,490)	(3,438)
Investing activities
Purchases of marketable securities	(135,376)	(121,016)
Maturities of marketable securities	121,250	70,705
Purchases of property and equipment	(1,514)	(1,430)
Net cash used in investing activities	(15,640)	(51,741)
Financing activities
Proceeds from public offering of common stock, net	78,693	40,099
Proceeds from the sale of common stock to collaborative partner		18,629
Proceeds from issuance of common stock under equity incentive plans	3,126	1,418
Net cash provided by financing activities	81,819	60,146
Net increase in cash and cash equivalents	21,689	4,967
Cash and cash equivalents at beginning of period	15,267	8,161
Cash and cash equivalents at end of period	$ 36,956	$ 13,128

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Description of Business	1. Description of Business Five Prime Therapeutics, Inc. (we, us, our or the Company) is a clinical-stage biotechnology company focused on discovering and developing novel protein therapeutics. Protein therapeutics are antibodies or drugs developed from extracellular proteins or protein fragments that block disease processes, including cancer and inflammatory diseases. We were incorporated in December 2001 in Delaware. Our operations are based in South San Francisco, California and we operate in one segment. Unaudited Interim Financial Information The accompanying financial information as of September 30, 2015 is unaudited. The Condensed Financial Statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. We derived the Condensed Balance Sheet as of December 31, 2014 from the audited financial statements, but did not include all disclosures required by generally accepted accounting principles in the United States of America, or GAAP. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying Condensed Financial Statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 filed with the U.S. Securities and Exchange Commission. Follow-on Public Offering In January 2015, we closed an underwritten public offering of 3,829,994 78.7

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions about future events that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements as well as reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates. Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any Level 3 securities as of September 30, 2015. The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands): September 30, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 31,653 $ 31,653 $ — $ — U.S. Treasury securities 146,458 146,458 — — Total cash equivalents and marketable securities $ 178,111 $ 178,111 $ — $ — December 31, 2014 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 9,996 $ 9,996 $ — $ — U.S. Treasury securities 130,786 130,786 — — U.S. government agency securities 3,001 — 3,001 — Total cash equivalents and marketable securities $ 143,783 $ 140,782 $ 3,001 $ — Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. We excluded the following options to purchase shares of common stock and restricted stock awards, or RSAs, (in thousands) from the calculation of diluted net loss per share for all periods presented as the effect would have been antidilutive: Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Options and RSAs to purchase common stock 3,499 2,404 2,926 2,253 3,499 2,404 2,926 2,253 Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers: Topic 606

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2015
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following is a summary of our cash equivalents and marketable securities (in thousands): September 30, 2015 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 31,653 $ — $ — $ 31,653 U.S. Treasury securities 146,421 38 (1 ) 146,458 178,074 38 (1 ) 178,111 Less: cash equivalents (31,653 ) — — (31,653 ) Total marketable securities $ 146,421 $ 38 $ (1 ) $ 146,458 December 31, 2014 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 9,996 $ — $ — $ 9,996 U.S. Treasury securities 130,785 18 (17 ) 130,786 U.S. government agency securities 3,001 — — 3,001 143,782 18 (17 ) 143,783 Less: cash equivalents (9,996 ) — — (9,996 ) Total marketable securities $ 133,786 $ 18 $ (17 ) $ 133,787 As of September 30, 2015, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 146,421 $ 146,458 Total marketable securities $ 146,421 $ 146,458 We determined that the gross unrealized losses on our marketable securities as of September 30, 2015 were temporary in nature. We currently do not intend to sell these securities prior to maturity and do not consider these investments to be other-than-temporarily impaired at September 30, 2015. There were no sales of available-for-sale securities in any of the periods presented.

Equity Incentive Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	4. Equity Incentive Plans The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Number of Exercise Price Remaining Shares Per Share Term Balance at December 31, 2014 2,684,812 $ 7.85 Options granted 877,988 $ 19.97 Options exercised (348,999 ) $ 6.61 Options forfeited (114,231 ) $ 8.73 Options expired (10,465 ) $ 8.03 Balance at September 30, 2015 3,089,105 $ 11.40 Options exercisable 1,496,574 $ 7.14 5.73 We have granted RSAs to certain of our employees. RSAs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are unforfeitable once fully vested. We based the fair value of RSAs on the closing sales price of our common stock on the grant date. The following table summarizes RSA activity under our equity incentive plans and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at January 1, 2015 24,000 $ 12.18 RSAs granted 1,461,230 $ 18.58 RSAs vested (2,000 ) $ 13.47 RSAs forfeited (8,760 ) $ 20.06 Unvested balance at September 30, 2015 1,474,470 $ 18.47 As of September 30, 2015, there were 2,020,024 shares of common stock available for future issuance under our 2013 Omnibus Incentive Plan. Stock-Based Compensation We calculate employee stock-based compensation expense based on awards ultimately expected to vest reduced by estimated forfeitures. We estimate forfeitures at the time of grant and revise forfeitures, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Research and development $ 1,537 $ 383 $ 2,642 $ 1,112 General and administrative 1,316 471 2,414 1,118 Total $ 2,853 $ 854 $ 5,056 $ 2,230 We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Expected term (years) 6.0-6.1 5.4-6.7 5.5-6.1 5.3-6.7 Expected volatility 71 % 85 % 71-73% 85 % Risk-free interest rate 1.5-1.9% 1.7-2.0% 1.4-1.9% 1.6-2.0% Expected dividend yield 0 % 0 % 0 % 0 % As of September 30, 2015, we had $13.7 million of total unrecognized compensation expense related to nonvested employee and director stock options that we expect to recognize over a weighted-average period of 3.2 years. Additionally, we had $23.7 million of total unrecognized compensation expense related to employee and director RSAs that we expect to recognize over a weighted-average period of 1.4 years.

Acquired Technology

Acquired Technology	9 Months Ended
	Sep. 30, 2015
Research And Development [Abstract]
Acquired Technology	5. Acquired Technology INBRX 110 LP In July 2015, we entered into a research collaboration and license agreement with INBRX 110 LP, or Inhibrx, to obtain (a) an exclusive, worldwide license to antibodies to glucocorticoid-induced tumor necrosis factor receptor, or GITR, for therapeutic and diagnostic uses, which we refer to respectively as licensed therapeutic products and licensed diagnostic products, and (b) an exclusive option, or the option, to obtain exclusive, worldwide licenses to multi-specific antibodies developed by Inhibrx that bind to both GITR and other targets, each of which we refer to as a multi-specific product. We can exercise an option with respect to a multi-specific product within a limited period of time after (i) certain activities related to initiating clinical manufacturing of such multi-specific product or (ii) if not earlier exercised, the dosing of the first patient in a Phase 2 clinical trial of such multi-specific product. Pursuant to the agreement, we paid Inhibrx an upfront fee of $10.0 million for the license and for services to be provided by Inhibrx related to a research cell bank. Additionally, with respect to each licensed therapeutic product, we will be obligated to pay up to $62.5 million in specified development milestone payments and (i) if such licensed therapeutic product does not receive a Breakthrough Therapy Designation from the U.S. Food and Drug Administration, or FDA, up to $280.0 million in specified regulatory and commercial milestone payments, or (ii) if such licensed therapeutic product receives a Breakthrough Therapy Designation from the FDA, up to $380.0 million in specified regulatory and commercial milestone payments. Inhibrx is also eligible for low double-digit tiered royalties on future product sales. We may pay all or a portion of milestone payments for development and regulatory events in shares of our common stock, subject to certain limitations and conditions. We would be obligated to register for resale under the Securities Act of 1933, as amended, or the Securities Act, any such shares of our common stock. We expense payments for the acquisition and development of technology as research and development cost if, at the time of payment, the technology is under development, is not approved by the FDA or other regulatory agencies for marketing, has not reached technical feasibility, or otherwise has no foreseeable alternative future use. In accordance with this policy, we expensed the $8.0 million that we determined to be related to the license upon our entry into the agreement in July 2015 as research and development expense. In accordance with the ASC 730, Research and Development Costs

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2015
Postemployment Benefits [Abstract]
Employee Benefit Plans	6 . Employee Benefit Plans We sponsor a 401(k) plan under which eligible employees may elect to contribute to the 401(k) plan, subject to certain limitations, up to the lesser of the statutory maximum or 100% of eligible compensation on a pre-tax basis. We pay the administrative costs for the plan. Effective January 1, 2015, we elected to match employee contributions to the 401(k) plan, or the Company Match, as permitted by the plan. We plan to make matching contributions on June 15 and December 15 each year in an amount equal to 50% of the amount contributed by the employee up to an annual maximum Company Match per employee equal to the lesser of (i) 4% of such employee’s compensation, or (ii) $6,000. We deliver the Company Match through the issuance of shares of our common stock. We delivered 13,720 shares of our common stock as the Company Match on June 15, 2015 and recorded 401(k) plan Company Match expense of $94,000 and $430,000 for the three and nine months ended September 30, 2015.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2015
Subsequent Events [Abstract]
Subsequent Events	7 . Subsequent Event On October 14, 2015, we entered into a license and collaboration agreement, or the FPA008 collaboration agreement, with Bristol-Myers Squibb Company, or BMS, pursuant to which we agreed to grant BMS exclusive global rights to develop and commercialize certain colony stimulating factor-1 receptor (CSF1R) antibodies, including our monoclonal CSF1R inhibiting antibody that we refer to as FPA008, and all modifications, derivatives, fragments, or variants of such antibodies, each of which we refer to as a Licensed Antibody. Under the terms of the FPA008 collaboration agreement, BMS will be responsible, at its expense, for developing products containing Licensed Antibodies, each of which we refer to as a Licensed Product, under a development plan, subject to our option, at our own expense, to conduct certain future studies, including registration-enabling studies to support approval of FPA008 in pigmented villonodular synovitis, or PVNS, and in combination with our proprietary internal or in-licensed compounds, including in oncology. BMS will be responsible for manufacturing and commercializing each Licensed Product and we will retain rights to a U.S. co-promotion option. We will continue to conduct the current Phase 1a/1b clinical trial to evaluate the safety, tolerability and preliminary efficacy of combining Opdivo ® Pursuant to the FPA008 collaboration agreement, BMS will make an upfront payment of $350 million to us within 30 days after the effective date. Additionally, we will be eligible to receive up to $1.05 billion in development and regulatory milestone payments per anti-CSF1R product for oncology indications and up to $340 million in development and regulatory milestone payments per anti-CSF1R product for non-oncology indications, as well as royalties ranging from the high teens to the low twenties, such royalties to be enhanced in the U.S. in the event that we exercise our co-promotion option. The FPA008 collaboration agreement is subject to review under the Hart-Scott-Rodino Antitrust Improvements Act, or the HSR, and we expect it to become effective upon the expiration or early termination of the notice and waiting period.

Description of Business (Polici

Description of Business (Policies)	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions about future events that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements as well as reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any Level 3 securities as of September 30, 2015. The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands): September 30, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 31,653 $ 31,653 $ — $ — U.S. Treasury securities 146,458 146,458 — — Total cash equivalents and marketable securities $ 178,111 $ 178,111 $ — $ — December 31, 2014 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 9,996 $ 9,996 $ — $ — U.S. Treasury securities 130,786 130,786 — — U.S. government agency securities 3,001 — 3,001 — Total cash equivalents and marketable securities $ 143,783 $ 140,782 $ 3,001 $ —
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. We excluded the following options to purchase shares of common stock and restricted stock awards, or RSAs, (in thousands) from the calculation of diluted net loss per share for all periods presented as the effect would have been antidilutive: Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Options and RSAs to purchase common stock 3,499 2,404 2,926 2,253 3,499 2,404 2,926 2,253
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers: Topic 606

Summary of Significant Accoun14

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Summary of Assets Recorded at Fair Value	The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands): September 30, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 31,653 $ 31,653 $ — $ — U.S. Treasury securities 146,458 146,458 — — Total cash equivalents and marketable securities $ 178,111 $ 178,111 $ — $ — December 31, 2014 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 9,996 $ 9,996 $ — $ — U.S. Treasury securities 130,786 130,786 — — U.S. government agency securities 3,001 — 3,001 — Total cash equivalents and marketable securities $ 143,783 $ 140,782 $ 3,001 $ —
Options and Restricted Stock Awards Excluded from Calculation of Diluted Net Loss Per Share	We excluded the following options to purchase shares of common stock and restricted stock awards, or RSAs, (in thousands) from the calculation of diluted net loss per share for all periods presented as the effect would have been antidilutive: Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Options and RSAs to purchase common stock 3,499 2,404 2,926 2,253 3,499 2,404 2,926 2,253

Cash Equivalents and Marketab15

Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2015
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following is a summary of our cash equivalents and marketable securities (in thousands): September 30, 2015 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 31,653 $ — $ — $ 31,653 U.S. Treasury securities 146,421 38 (1 ) 146,458 178,074 38 (1 ) 178,111 Less: cash equivalents (31,653 ) — — (31,653 ) Total marketable securities $ 146,421 $ 38 $ (1 ) $ 146,458 December 31, 2014 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 9,996 $ — $ — $ 9,996 U.S. Treasury securities 130,785 18 (17 ) 130,786 U.S. government agency securities 3,001 — — 3,001 143,782 18 (17 ) 143,783 Less: cash equivalents (9,996 ) — — (9,996 ) Total marketable securities $ 133,786 $ 18 $ (17 ) $ 133,787
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of September 30, 2015, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 146,421 $ 146,458 Total marketable securities $ 146,421 $ 146,458

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Option Activity under Equity Incentive Plans and Related Information	The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Number of Exercise Price Remaining Shares Per Share Term Balance at December 31, 2014 2,684,812 $ 7.85 Options granted 877,988 $ 19.97 Options exercised (348,999 ) $ 6.61 Options forfeited (114,231 ) $ 8.73 Options expired (10,465 ) $ 8.03 Balance at September 30, 2015 3,089,105 $ 11.40 Options exercisable 1,496,574 $ 7.14 5.73
Schedule of Restricted Stock Award Activity under Equity Incentive Plans and Related Information	The following table summarizes RSA activity under our equity incentive plans and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at January 1, 2015 24,000 $ 12.18 RSAs granted 1,461,230 $ 18.58 RSAs vested (2,000 ) $ 13.47 RSAs forfeited (8,760 ) $ 20.06 Unvested balance at September 30, 2015 1,474,470 $ 18.47
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows (in thousands) Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Research and development $ 1,537 $ 383 $ 2,642 $ 1,112 General and administrative 1,316 471 2,414 1,118 Total $ 2,853 $ 854 $ 5,056 $ 2,230
Schedule of Stock Option Weighted-Average Assumptions	We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Expected term (years) 6.0-6.1 5.4-6.7 5.5-6.1 5.3-6.7 Expected volatility 71 % 85 % 71-73% 85 % Risk-free interest rate 1.5-1.9% 1.7-2.0% 1.4-1.9% 1.6-2.0% Expected dividend yield 0 % 0 % 0 % 0 %

Description of Business - Addit

Description of Business - Additional Information (Detail) $ in Thousands	1 Months Ended	9 Months Ended
	Jan. 31, 2015USD ($)shares	Sep. 30, 2015USD ($)Segment	Sep. 30, 2014USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment | Segment		1
Issuance of stock, Shares | shares	3,829,994
Proceeds from public offering of common stock, net	$ 78,700	$ 78,693	$ 40,099

Summary of Significant Accoun18

Summary of Significant Accounting Policies - Summary of Assets Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets
U.S. Treasury securities and government agency securities	$ 146,458	$ 133,787
Total cash equivalents and marketable securities	178,111	143,783
Money market funds [Member]
Assets
Money market funds	31,653	9,996
U.S. Treasury securities and government agency securities	31,653	9,996
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities and government agency securities	146,458	130,786
U.S. government agency securities [Member]
Assets
U.S. Treasury securities and government agency securities		3,001
Level 1 [Member]
Assets
Total cash equivalents and marketable securities	178,111	140,782
Level 1 [Member] | Money market funds [Member]
Assets
Money market funds	31,653	9,996
Level 1 [Member] | U.S. Treasury securities [Member]
Assets
U.S. Treasury securities and government agency securities	$ 146,458	130,786
Level 2 [Member]
Assets
Total cash equivalents and marketable securities		3,001
Level 2 [Member] | U.S. government agency securities [Member]
Assets
U.S. Treasury securities and government agency securities		$ 3,001

Summary of Significant Accoun19

Summary of Significant Accounting Policies - Options and Restricted Stock Awards Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net (loss) income per share	3,499	2,404	2,926	2,253
Options and RSAs to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net (loss) income per share	3,499	2,404	2,926	2,253

Cash Equivalents and Marketab20

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 146,421	$ 133,786
Unrealized Gains	38	18
Unrealized Losses	(1)	(17)
Estimated Fair Value	146,458	133,787
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	31,653	9,996
Estimated Fair Value	31,653	9,996
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	146,421	130,785
Unrealized Gains	38	18
Unrealized Losses	(1)	(17)
Estimated Fair Value	146,458	130,786
Marketable securities including cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	178,074	143,782
Unrealized Gains	38	18
Unrealized Losses	(1)	(17)
Estimated Fair Value	178,111	143,783
U.S. government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		3,001
Estimated Fair Value		3,001
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	31,653	9,996
Estimated Fair Value	$ 31,653	$ 9,996

Cash Equivalents and Marketab21

Cash Equivalents and Marketable Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, In one year or less	$ 146,421
Amortized Cost Basis	146,421	$ 133,786
Estimated Fair Value, In one year or less	146,458
Total marketable securities, Estimated Fair Value	$ 146,458	$ 133,787

Cash Equivalents and Marketab22

Cash Equivalents and Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015USD ($)
Investments Debt And Equity Securities [Abstract]
Sales of available-for-sale securities	$ 0

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Option Activity under Equity Incentive Plans and Related Information (Detail)	9 Months Ended
	Sep. 30, 2015$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	2,684,812
Number of Shares, Options granted | shares	877,988
Number of Shares, Options exercised | shares	(348,999)
Number of Shares, Options forfeited | shares	(114,231)
Number of Shares, Options expired | shares	(10,465)
Number of Shares, Ending balance | shares	3,089,105
Number of Shares, Options exercisable | shares	1,496,574
Weighted-Average Exercise Price Per Share, Options beginning balance	$ 7.85
Weighted-Average Exercise Price Per Share, Options granted	19.97
Weighted-Average Exercise Price Per Share, Options exercised	6.61
Weighted-Average Exercise Price Per Share, Options forfeited	8.73
Weighted-Average Exercise Price Per Share, Options expired	8.03
Weighted-Average Exercise Price Per Share, Options ending balance	11.40
Weighted-Average Exercise Price Per Share, Options exercisable	$ 7.14
Weighted-Average Remaining Contractual Terms, Options exercisable	5 years 8 months 23 days

Equity Incentive Plans - Sche24

Equity Incentive Plans - Schedule of Restricted Stock Award Activity under Equity Incentive Plans and Related Information (Detail) - Restricted Stock Awards [Member]	9 Months Ended
	Sep. 30, 2015$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested, Beginning balance | shares	24,000
Granted, Number of Shares | shares	1,461,230
Vested, Number of Shares | shares	(2,000)
Forfeited, Number of Shares | shares	(8,760)
Number of Shares, Unvested, Ending balance | shares	1,474,470
Shares, Weighted-Average Grant-Date Fair Value balance at January 1, 2015	$ 12.18
Shares Granted, Weighted-Average Grant-Date Fair Value	18.58
Shares Vested, Weighted-Average Grant-Date Fair Value	13.47
Shares Forfeited, Weighted-Average Grant-Date Fair Value	20.06
Shares, Weighted-Average Grant-Date Fair Value balance at September 30, 2015	$ 18.47

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to nonvested employee and director stock options	$ 13.7
Unrecognized compensation expense expected to recognize, weighted-average period	3 years 2 months 12 days
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense expected to recognize, weighted-average period	1 year 4 months 24 days
Total unrecognized compensation expense related to employee and director RSAs	$ 23.7
2013 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock reserved for future issuance | shares	2,020,024

Equity Incentive Plans - Sche26

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 2,853	$ 854	$ 5,056	$ 2,230
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	1,537	383	2,642	1,112
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 1,316	$ 471	$ 2,414	$ 1,118

Equity Incentive Plans - Sche27

Equity Incentive Plans - Schedule of Stock Option Assumptions (Detail) - Options [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	71.00%	85.00%		85.00%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years	5 years 4 months 24 days	5 years 6 months	5 years 3 months 18 days
Expected volatility			71.00%
Risk-free interest rate	1.50%	1.70%	1.40%	1.60%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years 1 month 6 days	6 years 8 months 12 days	6 years 1 month 6 days	6 years 8 months 12 days
Expected volatility			73.00%
Risk-free interest rate	1.90%	2.00%	1.90%	2.00%

Acquired Technology - Additiona

Acquired Technology - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense related to license agreement		$ 24,720	$ 9,803	$ 49,241	$ 30,602
Inhibrx [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee paid for license and services	$ 10,000
Milestone payment method description				Additionally, with respect to each licensed therapeutic product, we will be obligated to pay up to $62.5 million in specified development milestone payments and (i) if such licensed therapeutic product does not receive a Breakthrough Therapy Designation from the U.S. Food and Drug Administration, or FDA, up to $280.0 million in specified regulatory and commercial milestone payments, or (ii) if such licensed therapeutic product receives a Breakthrough Therapy Designation from the FDA, up to $380.0 million in specified regulatory and commercial milestone payments. Inhibrx is also eligible for low double-digit tiered royalties on future product sales. We may pay all or a portion of milestone payments for development and regulatory events in shares of our common stock, subject to certain limitations and conditions. We would be obligated to register for resale under the Securities Act of 1933, as amended, or the Securities Act, any such shares of our common stock.
Research and development expense related to license agreement	8,000
Defer and capitalize amount related to prepayment of research and development cost	2,000
Recognized expenses on research and development		$ 400
Inhibrx [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration Fee, Payable	62,500
Inhibrx [Member] | Not Receives Breakthrough Therapy Designation [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Estimated regulatory and commercial milestone payments	280,000
Inhibrx [Member] | Receives Breakthrough Therapy Designation [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Estimated regulatory and commercial milestone payments	$ 380,000

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	Jun. 15, 2015	Jan. 02, 2015	Sep. 30, 2015	Sep. 30, 2015
Compensation And Retirement Disclosure [Abstract]
Eligible employees contribution percentage				100.00%
Defined contribution plan, employer matching contribution, percent of match		50.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay		4.00%
Defined contribution plan, employer matching contribution, amount		$ 6,000
Defined contribution plan, employer matching contribution, shares	13,720
Defined contribution plan, company matching contribution expense			$ 94,000	$ 430,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($)	Oct. 14, 2015	Sep. 30, 2015
Subsequent Event [Line Items]
License and collaboration agreement entered date		Oct. 14, 2015
Bristol-Myers Squibb Company [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Received upfront payment	$ 350,000,000
Upfront payment period	30 days
Bristol-Myers Squibb Company [Member] | Subsequent Event [Member] | Oncology Indications [Member] | Maximum [Member]
Subsequent Event [Line Items]
Development and regulatory milestone payments	$ 1,050,000,000
Bristol-Myers Squibb Company [Member] | Subsequent Event [Member] | Non-Oncology Indications [Member] | Maximum [Member]
Subsequent Event [Line Items]
Development and regulatory milestone payments	$ 340,000,000